rotating skybox

hi,erveryone
I want know how to rotate skybox in T3D, I only know that there is a function(_renderObject). What should do in this function. my code like follows:

EulerF rot;
	   rot.x = 0;
	   rot.y = 0;
	   rot.z = mRotatingAng;
	   mRotatingAng += 0.5f;

	   if (mRotatingAng > TWOPI)
	   {
		   mRotatingAng = 0;
	   }

	   QuatF rotQ(rot);
	   AngAxisF aa;
	   aa.set(rotQ);

	   aa.setMatrix(&mat);
	   mat.setColumn(3,pos);

	   sgData.objTrans = mat;

	   mMatrixSet->restoreSceneViewProjection();
	   mMatrixSet->setWorld( mat );

but it dose not work right. so I want know where is wrong in my code? Thanx in advance.